In conjunction with the design and testing of various products, e.g. consumer electronic goods and military products, vibration forces are applied to the product along selected axes thereof to determine if the product can tolerate such forces and continue to function properly. Because it is typically time consuming and somewhat difficult to attach and detach an object to be vibration tested to and from a vibration source, e.g. a shaker table, fixtures have been developed for facilitating the mechanical coupling the object with the vibration source. These fixtures generally comprise a base which is securely attached to the vibration source and at least one mounting surface to which the object to be vibration tested can be quickly and easily attached.
One such fixture is disclosed in British Patent Application No. 8,522,501, filed Sep. 11, 1985. This fixture has a cubic shape. The object to be vibration tested is attached to one face of the cube and another face of the cube is secured to a vibration source. By releasing the fixture from the vibration source after a vibration test is completed and rotating the cube about its diagonal axis 120 degrees, a new face of the cube is positioned for attachment to the vibration source. By this selective rotation of the cubic fixture, vibration forces can be selectively applied along three mutually-orthogonal axes of the object without the need for removing the object from the test fixture after each test. Rotation of the cubic fixture is effected either manually or by means of an electric motor.
Another vibration test apparatus is disclosed in U.S. Pat. No. 4,848,160, entitled "Multi-Axis Test Fixture System", issued on Jul. 18, 1989 to M/RAD Corporation of Woburn, Mass. (the assignee of this application). The latter apparatus comprises a cubic fixture for supporting an object to be vibration tested, a head expander positioned between the cubic fixture and a vibration source, an index assembly for raising the cubic fixture away from and lowering the cubic fixture onto the head expander, and a rotation assembly for rotating the cubic fixture about its diagonal axis when the fixture is raised above the head expander. The apparatus also includes a controller for automatically raising, rotating and lowering the cubic fixture so that vibration testing can be performed along three mutually-orthogonal axes of the test object without detaching the object or the cubic fixture on which it is supported from the vibration source during the three-test sequence.
The vibration test apparatus of U.S. Pat. No. 4,848,160 functions satisfactorily in most circumstances. However, where, for instance, objects are vibration tested in assembly-line fashion using unskilled or low-skilled personnel, it has been determined that the apparatus described in U.S. Pat. No. 4,848,160 can be too complicated for the average employee to operate. Accordingly, most vibration testing must be performed using fixtures which require detachment of the test object and/or fixture after a vibration test is performed along each of the axes of the object which are of interest. Clearly, where a multiple axis vibration test is to be performed, it is undesirable from a work efficiency perspective to attach and detach an object after the vibration test on each axis.
My prior copending application Ser. No. 07/731,372, now U.S. Pat. No. 5,156,051, discloses a vibration test fixture adapted for attachment to a conventional shaker table, or a conventional sliptable attached to a shaker table, which fixture is designed to support a test object so that the object can be vibration tested along three mutually-orthogonal axes in a single vibration test procedure without repositioning the object during the procedure. That test fixture is designed so as to simultaneously apply three equal vibration forces extending along mutually-orthogonal axes to a test object having mutually-orthogonal X, Y and Z axes so that the three vibration forces extend along or in parallel with a corresponding respective one of the X, Y and Z axes of the test object. The test fixture disclosed in said application Ser. No 07/731,372, now U.S. Pat. No. 5,156,051, comprises a flat object-supporting plate having a straight bottom edge and means for securing a test object in a selected fixed relationship on that plate so that the X and Y axes thereof form a 45.degree. angle with the bottom edge of the flat plate.
In one embodiment of the test fixture invention disclosed in my prior copending application Ser. No. 07/731,372, the flat object-supporting plate (and hence a test object secured to that plate) is inclined at about a 54.7.degree. angle with respect to the mounting surface of the shaker table to which the test fixture is secured. As a result of this inclination, the Z axis of the test object is inclined at about 35.3.degree. with respect to the mounting surface of the shaker table. In another embodiment of the invention disclosed in said application Ser. No. 07/731,372, now U.S. Pat. No. 5,156,051, the test fixture is secured to a slip table mounted to a shaker and is arranged so that its flat object-supporting surface (and hence a test object secured to that surface) is inclined at about a 35.3.degree. angle with respect to the mounting surface of the sliptable. As a result of this inclination the Z axis of the test object is inclined at about a 54.7.degree. angle with respect to the mounting surface of the sliptable. By so supporting the test object with respect to the mounting surface of the shaker table or sliptable, and thus with respect to the axis of the vibration force, each of three equal, mutually-orthogonal vibration force components of the input vibration force are coupled to the test object along or in parallel with corresponding respective ones of the X, Y and Z axes of the test object. The test fixture invention described and claimed in my prior copending application Ser. No. 07/731,372, now U.S. Pat. No. 5,156,051, has been a commercial success.